ML20248L369

Provides Addl Info to Support NRC Review of Supplement 1 to LARs 138 & 122,revising Licensing Basis for tornado- Generated Missile Protection Per Guidance in NUREG-0800. Probabilistic Risk Assessment Rept,Encl

ML20248L369
Person / Time
Site:	San Onofre
Issue date:	03/13/1998
From:	Rainsberry J SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20248L371	List: ML20248L369 ML20248L372
References
RTR-NUREG-0800, RTR-NUREG-800 NUDOCS 9803200037
Download: ML20248L369 (6)

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.. .Jk EDISON l souinsRN cAtironsir 1"s";tLenon, l An nisox isitassriopsi- a.mrun, March 13, 1998 l

U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:

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Subject:

Docket Nos. 50-361 and 50-362 l Additional Information Regarding Amendment Application Nos. 138 and 122 Use of NUREG-0800 Standard Review Plan Guidance in Evaluating Tornado-Generated Missiles San Onofre Nuclear Generating Station, Units 2 & 3

References:

1) Letter dated November 14, 1997, from Dwight. E. Nunn (SCE) to Document Control Desk (NRC),

Subject:

Docket Nos. 50-361 and l 50-362 Supplement 1 to Amendment Application Nos.138 l and 122, Use of NUREG-0800 Standard Review Plan Guidance in Evaluating Tornado-Generated Missiles, San Onofre Nuclear Generating Station, Units 2 and 3.

2) Letter dated August 19, 1992, from George Kalman (NRC) to l Harold B. Ray (SCE),

Subject:

Safety Evaluations for the Tornado Wind and Missile Loadings, Probabilistic Risks for the San Onofre Nuclear Generating Station, Unit No. 1 (TACNo.M63078)

This letter provides additional information in support of an NRC review of Supplement 1 to Amendment Applications 138 and 122 for the San Onofre Nuclear GeneratingStation, Units 2and3(Reference 1). This additional information concerning operator action time and the methodology for determining the .

probability of damage to critical equipment from tornado-generated missiles was requested by the NRC in a telephone conversation on February 19, 1998.

Supplement 1 to Amendment Applications 138 and 122 consists of Proposed Change Number (PCN) 433, Supplement 1. Supplement 1 to PCN 433 was a request to l revise the licensing basis for tornado-generated missile protection. The San Onofre Nudear Generating Station P. O.16 128 - l

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current licensing basis requires all critical components required to achieve safe shutdown following a design-basis tornado be protected. The proposed licensing basis allows for critical components to be exposed to tornado-generated missiles provided that the total per unit annual probability of damage to critical components from a tornado-generated missile strike is less than IE-7. This proposed licensing basis is based in part on guidance in NUREG-0800, " Standard Review Plan," Section 3.5.1.4.

OPERATOR ACT1Q81 NRC Request: How much time is required after receipt of a Severe Weather Warning to complete operator actions to isolate the Condensate Transfer Piping? Are there any other operator actions credited i l to limit the probability of damage to critical components?

Response

The time required to complete all actions required following a Severe Weather Warning, including dispatching an operator from the control room to isolate the Condensate Transfer Piping, is less than four hours. There is one other operator action credited, which is to close the Control Room Lobby Missile Doors.

Supplement 1 to PCN 433 states that the calculated probability of damage to critical components is dependent in part on operator actions. Specifically, PCN 433 states that:

"The probability of damage to exposed critical components as listed in the proposed UFSAR Table 3.5-13 is based in part on procedural actions which limit the area of exposed critical components _(e.g., isolating the Condensate Transfer Piping downstream of valves HV-5715 and 1414MUO92 on receipt of a Severe Weather Warning)."

This operator action to isolate the Condensate Transfer Piping is governed by l SanOnofreprocedureS023-13-3,"NaturalDisaster/SevereWeather,"

( Attachment 4, " Severe Weather Preparations," Step 2.10, " Maximize Condensate Inventory." Attachment 4 of S023-13-3 is entered when a severe weather L warning is received from the Southern California Edison Energy Control Center.

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Document Control Desk l l

Severe Weather notifications are usually issued 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> prior to the impending condition. The chronology of the steps in Attachment 4 is as follows:

Step Receipt of Severe Weather Warning Initiate S023-13-3, Attachment 4 Perform plant management notifications (Step 2.1)

Plant shutdown determination (Step 2.2)

Perform potential missile inspections (Step 2.3)

Ensureadequatestaffing(Step 2.4)

Restore important-to-safety systems to service (Step 2.5)

Isolate control room envelope (Step 2.6)

Verify 220 Kv electrical distribution system status (Step 2.7)

Verify the status of Class 1E distribution system (Step 2.8)

Verify the status of non-1E distribution system (Step 2.9)

Maximize condensate inventory (Step 2.10)

Sumps and liquid waste (Step 2.11)

Station blackout preparations (Step 2.12)

Final missile inspection (Step 2.13)

Preparations complete (Senior Reactor Operator /0perations Supervisor signoffonAttachment4)

The time required to perform Step 2.10 is less than 30 minutes. In accordance with Note 1 of Attachment 4, the steps of Attachment 4 are to be performed concurrently. It has been estimated that all actions required by Attachment 4

-can be completed within four hours of receipt of a Severe Weather Warning.

One other operator action, to close the Control Room Lobby Missile Doors, is credited to support the calculated probabilities of damage provided in Supplement 1 to PCN 433. The entrance to the control room lobby consists of two sets of double doors. One set is fire-rated and is normally closed as part of the control room envelope. The redundant set is missile-resistant and is normally open. Step 2.5 of Attachment 4 to 5023-13-3 requires that the Control' Room Lobby Missile Doors be closed. Again, all operator actions will i be completed within four hours of receipt of a Severe Weather Warning.

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l ()ocument Control Desk METHODOLOGY FOR DETERMINING PROBABILITY OF DAMAGE NRC Request: Explain why the methodology used to determine missile strike probabilities in PCN 433, Supplement 1 is applicable to Units 2 l and 3, and also whether this methodology has been previously approved by the NRC.

I Response: l 1

The methodology used to determine tornado missile strike probabilities in l Supplement I was based on a study performed by Erin Engineering and Research of tornado probabilities and tornado missile populations that was originally )

performed for Unit 1. '

The methodology for determining missile strike probabilities and tornado missile populations for Unit I was previously approved by the NRC in the i Safety Evaluation Report dated August 19, 1992 (Reference 2).

1 PCN 433 referred to an analysis for Units 2 and 3 (Tornado Missile Frequency )

Analysis, NSG 97-06) which determined annual probabilities of damage to i exposed critical components per square foot. NSG 97-06 (copy enclosed) was l based in part on data from the Erin Engineering study discussed above.  !

If you have any further questions on this subject, please call me.

Sincerely, 0k J. L. Rainsberry Enclosure cc: E. W. Merschoff, Regional Administrator, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3 S. Y. Hsu, Department of Health Services, Radiologic Health Branch i

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ENCLOSURE Tornado Missile Frequency Analysis, NSG 97-06

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REPORT No: [Yh:4 Nf6-17,06 Mini)<-. Qtim? NY^

QUAUTY ELEhENT SATISFIED QUAUTY ELDENT SATISFIED 08JECTNE References esist for:

No The obWive le ciesth en succinct $ eleted. t Y The version of the PRA model used.

Yesh 8ACKGROUNO M acuroes of plant design and proceduralinformation. Ye iNo-8eckground informaton is prowded which ciesth explans the No problem. a is wnnen so as to prowde compeans endence ther the enehet understands the systems and the problem. Legible M failure date. yeeQ muetratione are included where needed.

APPROACH Failure Date:

An _ _ _ _ _ prendes a clear overwsw of how the problem van be estected. (Pru.dr) in /beyrs W **m) fNo Plant.epecdic failure deLa are used whenever possible Ye d ANALYSIS Failure data are interpreted and applied propery Ye @

Annumptions:

M eseumptione necessary to support the solutice are cieerty sisted.

h Human ermr anahese have been formelh calculated. Y M meansngful damage states are coneadored

@lNo Common oeuse feelures have been canadered-Yee@

undeling Consdence:

Melhornetical equehone are appropriate and used properh No An uncertanly enseyese has been performed Yes Event trees and fault trose i. ,

system (s) and soonano(s). NtM(, rt 46/'

ro6ect the @h Yes A senestMiy enelyne hee been performed. Yee N Where ;=  ; faut trees and event trose have been utilized, they have not been blindly plugged in but have been Yh This enelyue le complete: there are no loose ende.

@ No checked to ensure that their loger,. .and CONCLUSION euccess NW are# g8o for this W%

, The conclusion le obsessive. e logioni reeuk of the anahuse. Ye fNo wg g and directh addreasse the " Objective" statement.

Modeling L._ , _ -iricke employed to models or trees for use in this study are emplemed in detail. ( Ye11@

EXPLANATION OF ALL "Noe ASOVE.

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